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# Determining the activation energy of a reaction, By using the experimental data and the Arrhenius equation, the activation energy for the reduction of peroxodisulphate ions, S2O82-(aq) by iodide ions, I-(aq) in a clock reaction is found to be approximatel

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Introduction

Determining the activation energy of a reaction Data Collection Table 1: Raw data - time taken for the mixture to turn blue-black in colour Temperature/?�1 30 35 40 45 50 Reaction completion time/second �1 152 99 76 46 44 Data processing Table 2: Processed results from Table 1 Temperature, T /K�1 K-1 Rate constant, K /dm3 mol-1 s-1 ln K 303 0.00330 0.00658 -5.02 308 0.00325 0.0101 -4.60 313 0.00319 0.0132 -4.33 318 0.00314 0.0217 -3.83 323 0.00310 0.0227 -3.78 Note: the rate constant, K is calculated as follows: Graph Note on graph: In this graph T is temperature in Kelvin and t is the time taken for the reaction to reach the blue-black colour stage. A R2 value is calculated in the graph above using Microsoft Excel. The R2 value - or the coefficient of determination, can be an indication of how closely the points relate to a line of best fit. It ranges from 0 to 1 with the latter indicating that the line of best fit can fully predict future points. ...read more.

Middle

However, it is assumed for this investigation that the uncertainty in time is �1 second. Assuming that uncertainties for the Universal Gas Constant, R, and Arrhenius' Constant, A, are zero, and taking the values associated with the median temperature of 313Kelvin we are left with the following limits of accuracies: Time = �1 OR To calculate the uncertainty of ln k, Time for the median temperature, 76 seconds, is taken. Thus, it can be seen that the uncertainty for ln k is approximately �0.01 or 0.231% Calculating the overall uncertainty The Arrhenius equation can be rearranged as follows: Since R and ln A are assumed to have zero uncertainty, the overall uncertainty can be calculated as follows: Uncertainty of T + uncertainty of ln k = 1.32% + 0.231% = 1.55% Overall uncertainty = Therefore, the activation energy is as follows: 52.9kJ mol-1�0.820 Conclusion By using the experimental data and the Arrhenius equation, the activation energy for the reduction of peroxodisulphate ions, S2O82-(aq) ...read more.

Conclusion

A way to improve the accuracy in data collection is to use greater concentrations of solutions so that the change in colour would be more instantaneous. However, for the purpose of this investigation the accuracy of the time recorded was assumed to be approximately �1 second. An improvement that can be made to the method is in the way the solutions are mixed together. In this experiment the two solutions are mixed manually. Although the way in which they were mixed was kept as constant as possible, a better method can be adopted to ensure that all the mixing is done uniformly. For example, a magnetic stirrer can be used in place of manual mixing - one can control the intensity and speed at which the solutions are mixed in this way. One way to develop this experiment further is to investigate in the effect of catalysts such as Fe2+ and Fe3+. Catalysts generally lower the activation energy, so it would be interesting to investigate in how Fe2+ and Fe3+ affect this particular reaction. 1 Eileen Ramsden (2000). A-Level Chemistry. 4th ed. London: Nelson Thornes. 169. ?? ?? ?? ?? Candidate Name: Teng, Eva Yi-Chun Candidate Number: 001407-038 1 ...read more.

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